This proposal is in response to our earlier histochemical finding that suggests that osteoblasts possess a highly active plasma membrane Ca++- translocating ATPase on the apicial and lateral (non-bone) sides of the cell. Since the role of this enzyme is outwardly-directed calcium translocation in all other cells that have been studied, it is expected that the Ca-ATPase in osteoblasts will also move calcium out of the cell. The ATP-hydrolyzing capacity of the Ca-ATPase, its Ca++ translocating properties and its regulation by substances known to stimulate osteoblasts will be examined in vesicles prepared from the plasma membrane of osteoblasts. In addition, demonstration of the existence of a Na/Ca exchanger and calcium channels will be sought. It is postulated that the Ca-ATPase exists on the apico-lateral sides of the osteoblast and that a Na/Ca exchanger may be present on the basal side of the cell. Two sources of osteoblasts will be utilized: (1) osteoblasts derived from neonate rat calvaria which represent intramembranous bone formation and, hence, the cranio-facial skeleton; and (2) trabecular bone of avian medullary bone, a highly metabolically active bone, which represents bone derived from the endochondral ossification process. The studies are intended to provide insight into mechanisms of osteoblast function, cells which are important in cranio-facial development, orthopedics and understanding diseases of bone loss in which decreased bone formation has been noted.